The reason the stores products do not have this issue is that stores often use extra preservatives in their salads. The mayo is almost always going to break down. I would continue to store it the way you have been, since everything tastes better after a day or two in the fridge. Just re-stir before serving. If it’s really excessive, I would use a paper towel ...
Make a bath of lye and soak items fully submerged.
Lye will dissolve anything organic, including mothers-in-law.
Lye is very caustic and will burn skin and damage eyes.
Wear gloves and eye protection.
It's also not very good for septic systems.
The water....but no need to be super precise. You should be able to taste the salt. Under or unsalted pasta water results in a flat tasting pasta. However, it is possible to over salt the water, resulting in over-salted pasta.