Dishwasher and washing machine waste is one of the most common under-sink connections there is, and one of the most annoying. The trap is in, the appliance is in, and the hose nipple is pointing at the back of the cabinet. This guide covers how to pick the right combination trap for the job so the hose lines up first time.
Where appliance waste usually connects
In most Australian kitchens and laundries, the dishwasher or washing machine discharges into the fixture's trap through a hose nipple on a combination trap (combo trap). It keeps the appliance waste on the same trap and water seal as the sink or tub, and avoids running a separate standpipe in a tight cabinet. For a full rundown of trap types, see our guide to combination traps vs P traps vs S traps.
The three things that decide which combo trap you need
1. How many hoses connect
A kitchen sink with a dishwasher needs one nipple. A laundry tub with a washing machine needs one. A kitchen with a dishwasher plus another appliance, or a combined laundry setup, needs two. A dual-nipple trap covers all of these – just cap the nipple you're not using.
2. Which direction the hose comes from
This is where most installs go wrong. Fixed-nipple combo traps point the hose connection in one direction. If the appliance sits on the other side of the sink, or the cabinet has a drawer runner, a false back or a bin pull-out in the way, the hose ends up tight, kinked or needing extra fittings.
The Twister trap combination solves this with two nipples that each rotate a full 360°. Twist them by hand to point at the appliance – before or after the trap is fitted – and the hose takes the shortest clean route.
3. How much height you have
Under-sink drawers, shallow cabinets and high-set wall wastes all reduce the height available for the trap. A standard-height combo trap can foul the drawer or sit below the waste point. That's when you need a low-level combo trap. The Twister converts to low-level by removing the extension piece, so one trap on the van covers both situations.
Fixed-nipple vs rotating combo traps
| Fixed-nipple combo trap | Twister rotating combo trap | |
|---|---|---|
| Hose nipples | Fixed angle | 2 × 360° rotating |
| Low-level option | Separate product | Remove the extension piece |
| Best for | Simple installs where the hose already lines up | Tight cabinets, drawers, appliances on the “wrong” side |
| Connections | Varies by product | Compression unions |
| Sizes at PSA | ACP DN40, ACP DN50 | 40mm (DOVMC40) and 50mm (DOVMC50) |
If the hose already lines up, a fixed-nipple trap does the job. If you're not sure what you'll find under the sink, the Twister is the safer one to carry, because it adapts on site.
40mm or 50mm?
Size the trap to the sink or tub waste outlet and the drain it connects to, not to the appliance. 40mm suits most laundry tubs and many kitchen sinks; 50mm suits larger or double-bowl sinks and wherever the existing drainage is 50mm. The Twister comes in both with the same rotating design.
Fit-off checklist
- Hose height and loop: follow the dishwasher or washing machine manufacturer's instructions for the drain hose high point, so the appliance can't siphon or back-fill.
- Secure the hose: clamp the hose onto the nipple and support it so it can't be pulled off by drawers or bins.
- Cap unused nipples: any nipple not in use must be capped.
- Check the unions: hand-tight plus a nip on compression unions. Don't over-tighten PVC.
- Test under load: fill and drain the sink or tub, then run the appliance through a pump-out and check every joint for leaks.
- Compliance: use WaterMark-approved traps, installed by a licensed plumber to AS/NZS 3500.2.
FAQs
Can a dishwasher drain into the sink trap?
Yes, that's what a combination trap's hose nipple is for. Fit the drain hose to the nipple and follow the dishwasher manufacturer's hose-height instructions.
Can a washing machine and a dishwasher share one trap?
A dual-nipple combo trap like the Twister has two hose connections. Whether both appliances can share one fixture trap depends on the installation, so check against AS/NZS 3500.2 and the appliance instructions.
What is a low-level combo trap?
A combination trap with a reduced overall height, used where drawers, shallow cabinets or a high wall waste leave less room under the fixture. The Twister becomes a low-level combo trap when the extension piece is removed.
Do the Twister's nipples stay where you set them?
Yes. You rotate them by hand to the position you want and they hold that position, so the hose can be connected without extra elbows.
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