I recently had major repairs done after a severe storm. The contractor dumped drywall compound and paint down the kitchen sink and used a whole box of Kleenex in the toilet. It wasn't just a final rinse of the tools and brushes but chunks of drywall compound, etc... We have a septic system with two separate injector pumps. The toilet already backed up and was able to be unclogged by just using a plunger. The contractor's master plumber said the Kleenex was not an issue and could be pumped out next time we had our tanked cleaned if it hasn't dissolved. He failed to address the drywall compound and paint issue. I have two questions:

1) is it unreasonable to be concerned by this? Can any of this cause damage to our injector pump or system and cause a future back up?

2) what, if anything, should I do now?

I could really use some advice. I don't want to be unreasonable but we just went through major repairs because of a storm and I am exhausted and couldn't handle a sewer back up a this point.

Any help would be greatly appreciated! Thanks so much.

Agree the Kleenex shouldn't be a problem. The drywall finisher must be an idiot to put dry wall mud in the plumbing. Even worse if you are on a septic system.
However, the drywall mud is water soluble and should dissolved. Any that does not dissolve and clumps up should settle to the bottom of the septic tank, to be remove the next time the tank is pumped.

If you have not had any problems by now, you are not going to. Just don't hire that dry wall finisher again.