[AlainTernet]

My detached garage construction will start in a weeks and I think to add running water for a sink in the garage. The garage will be at about 30' of the house (about 40-50' from where I can plug the drain and water line in the house). The digger man will make a 1 foot deep trench for electricity but I can ask to dig deeper like 4' to put water line and sewer.

1- I am in Quebec in Canada, and the frost line is probably more than 4' deep. I plan to put pipes only at 4' underground because the price for the trench jump after this deph and because the lowest foundation walls in the basement is about at 4' (if I want to go go deeper I should drill or dig into the floor and it's more complicated...) It seems easier for me to just drill a hole in the foundation wall, just a few inches above the floor of the basement and plug the sewer pipe into my main sewer pipe as you can see on the first picture join. If I add some inches of foam over pipes, do I can save a few feet of deph to avoid freezing?

2- The second idea is to make a 5" deep trench and drill and dig on the floor to connect the sewer pipe more deep into the ground (see picture) but this is more complicated and more a messy job in the housse...

3- A 4" sewer white pipe it is ok for this ? (I can go for less than 4" but from what I understand from the plumber the necessary slope for a 4" pipe (1/8 by foot) is less than for a 3" one (1/4 by feet)

3- Do copper pipe is the best ? I can make the run without join if I buy I big 60' roll. it is better to use PEX ? Somebody tell me to put copper in a PVC or ABS pipe to avoid oxidation... ?

Your advice is welcome ! (and sorry for my poor english)

[phishfood]

I don't know anything about protection from freezing in colder areas with frost lines, so I can't comment on that.

As far as the copper, that should work well for what you wish to do. Unless the soil is really corrosive, you shouldn't need to run the copper inside of a sleeve.

If you use 4" pipe, the T fitting that you have circled in your last picture will have to be changed out to a 4" T. And if you use white (PVC) pipe, you will not be able to glue the black ABS and the white PVC pipe together, so you will need to plan for a mechanical joint there, perhaps a rubber coupling.

[Mr_David]

Ditto on frost protection knowledge. Looks like you've done some previous research. Nice drawings

If all you are installing is a sink a 2" line should be okay.