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Are there any disadvantages to adding a toilet so that the toilet waste drains into the washing machine drain? We have a small home and it only has one toilet. There are four people who live here so we are looking to maximize our space by adding a toilet in the garage. Is this possible? Any pitfalls?

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Not possible, don't even think about doing that. A toilet requires a 3 or 4 inch drain minimum. Also, you need a permit to install a toilet in every place I have ever heard of. – shirlock homes Apr 18 '12 at 23:41
I love a Humanure toilet, but I get that it's not for everyone. – Jay Bazuzi Apr 19 '12 at 1:56
have you got any photos of the proposed location and existing piepwork? – UNECS Apr 19 '12 at 6:41
@JayBazuzi: Just looked that up. While simple, I don't think my Wife would enjoy the smell too much :) That would be a last resort. – Brian Apr 19 '12 at 12:10
Don't do it! toilet waste pipe is significantly larger than a standard washing machine waste for a very good reason! – Matt Jun 30 '13 at 22:14
up vote 3 down vote accepted

a toilet needs either a large drain pipe or a fecal grinder that prevents fecal matter and toilet paper from clogging it up

that or it needs to be a urinal

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It depends what the size of the drain going to the washing machine is. As mentioned it should be put through your local authority but if your drainage under the washing machine is accessible and at least 3" it is possible. Running the toilet straight into the wash machine drain isn't possible if it discharges through a floor waste (gully).

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