Laundry drain conundrum - drain CWM into bathtub?
Pardon my ignorance - I'm a professional computer geek, not a plumber.
I recently bought a condo apartment in Seattle and want to install a compact ventless clothes washer dryer combo unit to avoid trips to the basement laundry room. (Nothing in the bylaws limits my right to do this, fortunately.)
Naturally, the drain's the rub.
I have a walk-in closet that happens to be directly under the water heater (overhead in the storage loft so access to hot and cold supply is not a problem) and shares a common wall with the foot of the bathtub.
This gave me the idea of fixing the drain hose to a "dummy" tub spout (or otherwise running the hose through the wall) to drain into the bathtub. It seems like this would adequately provide for an air gap and the tub's ample capacity (many times that of the small front-loading washing machine) would adequately buffer the drainage flow over time.
Would this be a realistic alternative to spending many kilobucks cutting willy-nilly into the walls and/or subfloors to find and plumb into drains and vents? If not, why not?
You found the best solution possible
I admire your ability to hit on the right solution considering all the constraints. In a little while you may have figured out how to get the drain hooked into your bathtub plumbing so you won't need to break the drywall (or tile) to put a hole in the wall to let your washer dryer drip into the tub. This will bypass the tub, but still make noises since it will put the water into the drain above the tub's P-trap (siphon). Technically still not up to code.
To get to code, you'll need another P-trap, at any height you like, with its drain going into the tub's drain below (downstream, past) the tub's P-trap. Assuming your condo building is not so big that the code would ask for a separate drain line for the Washer-dryer. Since a person can only have so many drains on a single line of a certain diameter before they are required to run a new separate line or else replace the entire line with a wider diameter pipe. And a washing machine counts for more "Units" than just a sink.
So in practical terms your washer might just cause the drain line to be overloaded some day when everyone else is draining their tub or shower. It could happen. That is what code is for. Nonetheless, don't let me scare you off. I'm just sharing with you the information I think I know, trusting that you will soon find it out anyhow some other way, and that you will make your own judgements and assessments.
Same size diameter for Tub drain and washing machine drain
Seems like neither one of us is an expert on the plumbing Code.
I do know this much: the diameter (i.e. size) of a drain is designed by code to be truly sufficient and even a little bit too much in order to handle the worst situations. Each drain is the size it is for a reason. I also know that it is against Code to put in a drain that is two or three sizes larger than the prescribed size. I also know that a 1.5" diameter drain is the size for 1. a tub, 2. tub-shower cominations, 3. a washing machine, and 4. a washing machine with a laundry sink nearby plumbed into the same drain. I also know that each available size carries about twice as much volume as the smaller size pipe.
So I conclude that it is against Code to use a 3" pipe as a drain for a tub or a washer. Hope this helps.
All washing machines drain into a pipe which is 1.5" in diameter. The 1.5" diameter pipe that is already in place, for the tub, is the same pipe. When a tub drain AND a washer drain, both 1.5", combine, the next size up, 2", is used to carry the two drain flows together. That 2" pipe flows into a bigger pipe whic carries your waste water with other neighbors' too.
Also, please realize that copper sweat solder is not a challenge, and drains do not carry pressurized water which is the kind that causes floods. Flooding is not a risk. You can make a seal with copper, and let drain water flow though the pipe, without worrying about a future flood. You can inspect your seal visually. You can test run it. You can keep coming back to it and checking for minor leaks. That is the extent of the risk. My opinion.