That’s executive functioning failure. It’s common with ADHD (which is strongly comorbid with Autism) but not unique to it.
Basically, the part of your brain dealing with task focus is either asleep or exhausted. At that point, you are running on pure impulsiveness.
If you get locked in, the best bet is to stop banging your head against a brick wall. Stop trying to do the big task, that is stressing you. Instead aim for a small, neutral or positive task to lock on to. E.g. throwing together a sandwich, or going to the loo, rather than “I REALLY need to get my taxes done!” It’s a far from perfect method (it still fails often), but it does help kickstart you back to higher brain thinking.
It depends on the hose and the flow rate. They can vary a lot.
Also, your not just clearing the stagnant water, but also anything that was growing in it.