Hi,
I want to move the washing machine to the bathroom - single storey building, wooden frame. The washing machine (front loader) will be next to the bathtub.

Question about the right way of drain for the washer:
- can I connect to the existing bathtub drain? If so - what is the best option: standpipe with a trap and a Y-connector; Trap with a spigot to connect the drain hose directly (which I think might back up); Is there a need some separate vent?

- I can connect to the main drain pipe under the house - but would this need to add a vent pipe (not keen on going through the roof) - or a standpipe and Y-connector will be OK?

- are there other options to do it?

All pipes are plastic, house some 10 years old (NZ code).

Thank you,

 

Plumbers should be in soon. Washer usually require a 2 inch drain line and must have a trap in the line. Also the drain pipe must be higher than the highest level of water in washer.

 

Just to get this out of the way first, most of the suggestions you'll get here are related to US code. I for one, don't know how similar they are in New Zeland, so you may want to discuss with someone there. But that said...

Washers do require a 2" standpipe and drain. Especially newer front-loading washers tend to expel a lot of water quickly and can overwhelm a 1.5" drain. Most bath tubs are plumbed with 1.5" drains.

So that leaves you with cutting into your main drain. You'd have to wye off your main drain under the house, come up vertically through the floor. At a few inches above the floor, you add a sanitary tee, to a p-trap, and the standpipe. Above the sanitary tee, you can likely use an air admittance valve (AAV) instead of venting through the roof - but they are allowd in some locales and not in others.

Something like this: