If it was a yellow paste, I'm guessing it might have been pyrantel pamoate.
Knowing what species of nematodes would help a lot because there are so many different kinds. Pinworms are no big deal but tend to be species-specific so I doubt the mice could have transmitted those to your snake. (It's possible to find mice pinworm eggs in your snake poop but that doesn't mean the snake was infected with those pinworms.) However, hookworms and strongyloides can hop from species to species. They are the reason why you don't want to go traipsing barefoot on your lawn. The larvae burrow through your skin, continue burrowing, and even after they infect you, they still burrow and cause blood loss. They're extremely common in reptiles and often don't cause any outward symptoms.
Luckily, nematodes are pretty easy to clean after. The key is to clean OFTEN--ideally every time after your snake poops or at least once a day. This is really important because your snakes could very well reinfect themselves. Cat-dog vets don't emphasize this very much because their patients aren't living in cages. The medicine is only effective against the adult worms, so there are probably eggs and larvae still cycling through the snakes, hence the need for a second and sometimes third dose of medicine.
A good washing with dishwasher soap and water is enough to do the job. I'm really weary of using bleach because even if you air out the cage, there's still enough residue vapor to harm the snakes. At the very minimum you should change the substrate, but wash everything in the cage everyday if you can.
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