Can you still do some prn work if you take the desk job? In my opinion, you should work while you can now to earn what you can now, and take the experience while there are opportunities. Later, you can get the desk job, but for more money, since you’re more experienced. Also, there are opportunities in research/real world evidence/device manufacturers/ software companies outside the healthcare systems for experienced clinicians like yourself (even fully remote ones).
Maybe this current role isn’t perfect for you, but it started you wondering, and that’s good.
I have a standing every 2 years on each of my 2 10k gallon tanks. Each year, one gets pumped. That means they both get checked regularly.
Even if it costs $200 for the appointment, it’s worth it to know. They can also likely tell you the size and what they suggest for your situation. They should be able to schedule it for you so you don’t need to remember.
FWIW, ask around to find a reliable, honest septic service provider. Ask your neighbors. Ask your plumber. Ask at the hardware store (if you have an independent or franchise, not a big box. Ask at the plumbing supply store.