You are absolutely correct but that is why hiring a contractor is more expensive than doing it yourself.

I was a general contractor in Florida. The costs for, insurance, continuing education, permits, etc ran me out of business.

You just described the whole construction industry.

I love my restaurant supply knives. Better than my expensive ones in MHO.

Funny, I own Wusthof, and Chicago Cutlery. My favorite knives are the ones that I buy at the restaurant supply for cheap.

I was trying to give OP a quick and dirty example to get them in the ballpark. We haven't even considered voltage drop in the wire or the start up current draw. If I was installing this circuit based on the 3600 watt example I would be designing, based on experience, for a minimum 50 amp breaker.

Now I admit, I'm not an electrical engineer or even an electrician. I'm just a lowly PMEL tech who calibrates and repairs all of the test equipment.

Funny, I was taught to use RMS.

To figure current from wattage divide the number of watts by the voltage. 3600 watts / 120 volts = 30 amps

https://www.acehardware.com/departments/paint-and-supplies/chemicals-and-cleaners/adhesive-removers/1595826?x429=true&msclkid=b4f7bc032d3e19b22eb8df609b0d4e3d&gclsrc=ds&gclid=CImu9YCEkvsCFYwTgQodeZgLxg&gclsrc=ds

Here in the states Home Depot sells a product that does what you want. Go to your local lumber yard and ask.

Spray it with a bit of bleach and see what happens.

Yes, a macerator and pump will work. I'm building a restaurant right now and the city install a macerator pump along with a 2" line.

Rent a grinder with a vacuum. Most of the big rental companies have them. Depending on how bad the floor is you may not need leveler when you are done.

12ga wire is rated for 20amps. more than likely the washer pulls less than 15 so 12ga is fine.

Ask for a pre construction meeting with the inspector. Now you can ask him your questions.