stupid question

Are you relying on the idiot lights to tell you it is empty? They are seldom correct.

That said, the only time I try hard to get them empty is before winterizing. Mainly so I don't dilute the pink stuff I leave in them.

(oops, guy above me says the same thing!)

First, no such thing as a stupid question....If you are going by the indicators inside...don't always work. Your tank could be empty but still registering that it has something in it, mine does it all the time. I look and then it shows empty. Sometimes pieces of paper get on the probes.. I try to dump some of my dishwater in my black tank on just about every outing. A lot of people put a bag of ice in there...jostle it around some while towing, helps to clean. I don't know where you live but you can always add enough RV Anti-freeze in there to help for winterization. Just my thoughts...

Part of the answer to your question lies in the placement of the drain within your holding tanks. In our case the black tank is furtherest to the rear of the coach, then the grey tank. The black tank drain is toward the hitch side of the black tank, so a "nose down" attitude helps the black tank drain more completely. The reverse is true for the grey tank.
We generally dump & flush tanks while still in the site, if we have sewer and if the TT is level front to back & side to side I'll get good drainage, with maybe a couple of quarts left in either tank. You'll want to do some exploring to see where each of your tanks empty.

Dump stations - I've seen way too many that are backwards, that is they tilt away from the dump valves and/or are sloped front to back. Because of this I almost always plan our trips where our final site has sewer hook-ups. That way I can thoroughly rinse my tanks without holding anybody else up.

Many years ago I invested in a Sewer Solution because our TT sits very low. As a previous reply to your post mentioned it is not unusual to have a sewer hook-up that is higher than your dump valves. The SS uses a water hose and a venturi effect to literally pump the waste water out. Works great and and the only moving part is a lever that directs the water jet into the dump valve to help backflush.

If I want a good dump I do use the levelers to tilt the trailer toward the drain.
Certainly not needed every time.

Side to side often helps - nothing extreme. It also helps to have the waste tanks as full as possible when you dump them. If your campsite has a water hookup, you might consider putting more water down the drains & toilet prior to dumping. Sometimes dump stations have kind of an indent that the trailer wheels fit in, which helps give you more of a side to side lean; if the CG you're staying at has a dump station (even if you have full hookups at your site), you might walk by it during your stay and see if it looks like it would help to use that, rather than dump in your site. We have often done that if the sewer hookup at our site is above-grade or has other issues that make dumping more difficult.

No really stupid questions here. Ask away - that's how you learn! :)