What are expert tips for drain assembly & garbage disposal connection?

Slip-joint connections are hand-tight plus a quarter turn with pliers. That's it. Cranking them down strips the plastic threads or cracks the nut. Always orient the tapered washer correctly: tapered side faces into the fitting, flat side toward the pipe. Backwards washers leak immediately. The simultaneous fill-and-release test catches problems that a slow trickle test misses. Fill both bowls full, pull both stoppers at once.

What mistakes should I avoid with drain assembly & garbage disposal connection?

Using silicone instead of plumber's putty on the basket strainer -- silicone makes future removal a nightmare. Overtightening slip joints until the plastic cracks. Installing the tapered washer backwards. Not sloping the horizontal pipes toward the wall drain, which causes standing water and odor.

Drain Assembly & Garbage Disposal Connection

Overview

The drain assembly is where most sink leaks happen, and it's usually because someone either skipped the plumber's putty or overtightened a slip joint. Whether you're setting up a single bowl with a disposal, a double bowl with one side disposal, or a straightforward drain without a disposal, the principles are the same: putty the flanges, hand-tighten the slip joints, and make sure every connection slopes toward the wall drain.

What to Know

Single Bowl with Disposal

The disposal mounts directly to the sink flange and replaces the standard strainer basket. The discharge tube from the disposal connects to a P-trap, which runs to the wall drain. Simple, direct path.

Double Bowl with Disposal

Usually the disposal goes on the side closest to the wall drain. The other side has a standard basket strainer. Both drains connect with a tee or continuous waste kit that joins them into a single P-trap. The non-disposal side's tailpiece connects to the disposal side's discharge via a tee fitting.

Double Bowl without Disposal

Both sides have basket strainers and tailpieces that join with a center tee or an end-outlet tee fitting, then into a single P-trap. The key is making sure both bowl drains slope toward the tee so water doesn't sit in the pipes.

Tools & Materials

Plumber's putty
Basket strainer assembly
Slip-joint pliers
Adjustable wrench
Hacksaw (for cutting tailpieces to length)
P-trap kit (1-1/2 inch is standard for kitchen sinks)

Step by Step

Install the basket strainer(s)
Roll a thick rope of plumber's putty and press it around the drain opening from above. Drop the strainer into the opening, pressing it into the putty. From below, add the rubber gasket, cardboard washer, and lock nut. Tighten until putty squeezes out evenly. Wipe excess putty from above.
Install tailpieces
Thread the tailpieces into the strainer body or disposal discharge. For double bowls, cut tailpieces to length so they meet the tee fitting at the correct height. The disposal side is usually shorter since the disposal discharge sits lower.
Connect the tee fitting (double bowl)
Slide the tee onto the tailpieces with slip-joint washers oriented correctly (tapered side facing the fitting). The branch of the tee connects the two bowls, and the outlet leads to the P-trap.
Install the P-trap
Connect the P-trap to the tee outlet (or directly to the tailpiece for single bowl). The other end of the P-trap connects to the wall drain stub. The trap should be at the correct height -- if it's too low, the tailpiece needs to be longer.
Test for leaks
Fill both bowls with water and release them simultaneously. This puts maximum flow through all the joints at once. Check every slip joint for drips. Tighten slightly if needed -- slip joints seal with compression, not torque.

Pro Tips

Slip-joint connections are hand-tight plus a quarter turn with pliers. That's it. Cranking them down strips the plastic threads or cracks the nut.
Always orient the tapered washer correctly: tapered side faces into the fitting, flat side toward the pipe. Backwards washers leak immediately.
The simultaneous fill-and-release test catches problems that a slow trickle test misses. Fill both bowls full, pull both stoppers at once.

Mistakes to Avoid

Using silicone instead of plumber's putty on the basket strainer -- silicone makes future removal a nightmare.
Overtightening slip joints until the plastic cracks.
Installing the tapered washer backwards.
Not sloping the horizontal pipes toward the wall drain, which causes standing water and odor.

When to Call a Pro

Sink drain assembly is beginner-friendly DIY. Call a plumber only if the wall drain stub is corroded, at the wrong height, or if you need to move it to accommodate a different sink configuration.

Bottom Line

Sink drain assembly is mostly about putty, proper washer orientation, and not overtightening. Fill-and-release test both bowls simultaneously. If everything holds dry, you're done.