Yes Presoak. Napisan is specifically for this and you can also add to the drawer of W machine
But also maybe buy more pants and wash the pooey ones together away from other laundry for a bit??
Biological washing powder (specifically Ariel) much much more fresher smelling if a bit harsh on clothes and skin IME
HTH and remember, this too will pass.
(usual MNHQ disclaimer about other laundry treatments being available)