There are repairs that people can do by themselves, but Josh lacks the resources and - most importantly - the patience to do the job right. With as frustrated as he is already, it will be easy for him to say screw it and cut corners to get the job done ASAP.
Most people, even if they're patient and careful, and good at following instructions, are going to make at least one critical mistake the first time they attempt a job like this because there is always some detail they miss because they didn't know to do it—and it's usually something small that pros have learned about on the job. Been there, done that.
Josh is not patient, careful, or good at following instructions.
If you have the money, you get a pro in to fix your mistake and explain what you unknowingly omitted, or did wrong. Or, if you're like me, you just pay them to do that job right from the start, and make up for it by DIYing everything else. Because if you screw up a job like plumbing, fixing it may end up costing more than the original job would have, especially if it forms slow leaks where you can't see them.
But if you're like Josh, and don't have money, your only fallback is going to be the goodwill of whichever pro/skilled DIYer you've got in your social circle—and Josh, being a hotheaded fuckwit, has already blown that.
Plus, they have no idea what the true state of the septic system is. Polissa's been flushing rock salt into it because she thinks there are tree roots causing her toilets to drain slow, but, as I've already sperged about, that's not how septic systems work. At bare minimum, the tank needs to be pumped (~$300), and, ideally, the system should be inspected (another $300). But God help them if any part of the septic system has failed, because nobody else will. Septic repair is $$$$$, and replacement is even more, and they will literally be shit outta luck.
