A garbage disposal mounts under the kitchen sink, intercepting food waste before it enters the drain plumbing. The install combines plumbing (drain modifications) and electrical (120V dedicated circuit, sometimes hardwired, sometimes plugged in). The job is a Advanced DIY because of the simultaneous trades, but standard for confident installers.
This guide covers a like-for-like replacement (existing disposal swapped) and adding a disposal to a sink that doesn't have one (more involved). Note: in some Ontario jurisdictions, garbage disposals are restricted or require permits — verify with local plumbing inspector.
- Skill level
- Advanced
- Time
- 1–3 hr
- Steps
- 9
- Tools
- 8, listed below
- Materials
- 7, listed below
Before you start
Three things to settle:
1. Check local code. Some Ontario municipalities restrict garbage disposals due to water treatment plant capacity. Verify whether disposals are allowed in your area. Where allowed, they typically require permitting if newly installed.
2. Disposal type and HP rating. 1/3 HP: light-duty, suitable for one-person households. 1/2 HP: standard residential. 3/4-1 HP: heavy-duty, larger families and frequent use. Higher HP means smoother grinding and less chance of jams. Lifespan: typical disposal is 8-15 years.
3. Plumbing changes. Adding a disposal: requires modifying the existing sink drain plumbing (T-fitting and tail piece replacement). Replacing existing: connections may not match exactly between brands; expect to swap drain components.
What you'll need
Tools
- Slip-joint pliers
- Adjustable wrench
- Phillips screwdriver
- Drill (for installing electrical box if needed)
- Voltage tester
- Bucket and old towels
- Hammer (for snapping out the disposal's dishwasher inlet plug, if applicable)
- Plumber's putty
Materials
- Garbage disposal (matching HP rating to needs)
- Mounting kit (typically included)
- P-trap and slip-joint connectors (for drain modifications)
- Dishwasher discharge tube (if disposal connects to dishwasher drain)
- Plumber's putty
- Wire nuts (for electrical connections)
- Plumber's tape
Don't put bones, fibrous vegetables, or grease down a disposal
Garbage disposals are designed for soft food waste — fruit and vegetable scraps, eggshells, small bone pieces.
Avoid: large bones, celery and corn husks (fibres tangle), grease (clogs drains downstream), pasta and rice (expand and clog), coffee grounds in large quantities, eggshells in large quantities.
Following these rules extends disposal life from 5 to 15 years and prevents drain clogs.
Step-by-step instructions
Turn off power and water
Switch off the breaker for the disposal (or unplug if cord-connected).
Verify with voltage tester at the existing disposal's connection.
Place towels under the sink — the existing disposal will have residual water.
Disconnect existing disposal (if replacing)
Disconnect the dishwasher discharge tube and the main drain hose.
Disconnect electrical wires (junction box on the disposal's underside).
Use the disposal's mount lock — most have a metal locking ring that twists to release the unit from the sink-mount flange. Twist counterclockwise; the disposal drops free.
Remove old sink-mount flange (if needed)
If the new disposal uses a different mounting system, remove the existing sink-mount flange. The flange is held by a nut underneath the sink.
Loosen the nut, drop the flange. Clean the sink's drain opening of any old plumber's putty.
Install new sink-mount flange
Apply a rope of plumber's putty (1/4 inch diameter) under the new sink-mount flange.
Drop the flange into the sink's drain opening. From below, install the supporting hardware (gasket, mounting ring, snap ring) per the disposal's instructions.
Tighten the mount until the flange seats firmly against the sink.
Wire the new disposal
Open the disposal's electrical compartment (usually a small plate on the underside). Connect the cable's wires to the disposal's wires:
Black to black (hot), white to white (neutral), green or bare to ground.
Use wire nuts. Pull-test connections.
Hang the disposal on the mounting ring
Lift the disposal up to the sink. Align with the mounting ring on the bottom of the sink-mount flange.
Twist the disposal's locking collar clockwise until it engages and locks. The disposal hangs from this connection.
Connect the dishwasher discharge tube (if applicable)
If a dishwasher discharges into the disposal, knock out the dishwasher inlet plug on the disposal (per instructions — usually a hammer + screwdriver to punch out the plastic plug).
Attach the dishwasher discharge tube to this inlet with a hose clamp.
Modify drain plumbing
The disposal has a drain outlet on its side. Connect this to the sink drain plumbing using a T-fitting and slip-joint connectors.
If you have a double-bowl sink, the disposal connects to one bowl's drain; the other bowl drains into the same T-fitting at a different angle.
Reconnect the P-trap to the new T-fitting.
Restore water and power, test
Turn on the breaker. Run the disposal — should spin freely with no grinding noise.
Run water and operate the disposal for 30 seconds. Check all connections for leaks.
Drop a small amount of food (peel from a vegetable) into the disposal to verify grinding action.
Common mistakes that cost you
- Wrong HP for household use. Underpowered disposals jam frequently. Match HP to household size and use frequency.
- Forgetting to remove dishwasher inlet plug. Dishwasher backs up because water can't enter the disposal. Punch out the plug before connecting dishwasher discharge.
- Not checking local code. Some Ontario municipalities restrict disposals. Verify before buying.
- Loose drain connections. Slip-joint connections need correct gaskets and snug tightness. Hand-tight plus a quarter turn — don't crank.
- Working with power on. Always verify off with a tester before electrical connections.
Frequently asked questions
Are garbage disposals allowed in Ottawa?
Generally yes, but specific bylaws vary. Verify with City of Ottawa or your local plumbing inspector before installing.
Some condo buildings restrict or prohibit disposals. Check building rules if applicable.
What can't I put down a disposal?
Avoid: bones (especially large/cooked), fibrous vegetables (celery, corn husks), grease, pasta and rice (expand and clog), coffee grounds in large quantities.
Disposals are designed for soft food scraps. Following these rules extends life significantly.
What HP rating do I need?
1/2 HP for typical 2-3 person household. 3/4-1 HP for families of 4+ or frequent cooking households.
Higher HP is quieter (less torque required to grind), grinds faster, and jams less frequently.
Why does the dishwasher back up after installing a new disposal?
A dishwasher backs up after a new garbage disposal install when the dishwasher inlet plug was never removed. The plastic plug in the disposal's dishwasher inlet blocks water from the dishwasher. Before connecting the dishwasher discharge tube, knock the plug out with a hammer and screwdriver as the instructions describe, then attach the tube to the inlet with a hose clamp.
Missing that step is one of the most common disposal install mistakes.
How is a garbage disposal connected to the sink drain?
The garbage disposal's side drain outlet connects to the sink drain plumbing through a T-fitting and slip-joint connectors, and the P-trap reconnects to the new T-fitting. On a double-bowl sink, the disposal drains one bowl and the other bowl drains into the same T-fitting at a different angle.
Slip joints need the correct gaskets and should be hand-tight plus a quarter turn. Once water and power are back on, run the disposal for 30 seconds and check every connection for leaks.
When to call us instead
If you're adding a disposal where one didn't previously exist, the plumbing modifications and electrical work may require permits. We do this as part of kitchen renovations.
Book a free 60-minute site visit →Dream Touch Renovations · 33 Roydon Pl, Suite 210, Ottawa, ON K2E 1A3 · (613) 862-4555
Renovating homes across Ottawa, Kanata, Nepean, Barrhaven, Orléans and Stittsville.
Related Ottawa services
If you're updating kitchen plumbing and appliances, our kitchen renovation team handles appliance installation as part of fixed-price scopes. Book a free 60-minute consultation.
Official references
- Do I need a building permit?, City of Ottawa
- O. Reg. 163/24: Building Code, Government of Ontario