Hello! I'm new EVe
Where is the valve for black tank Nd grey? I found one, but toilet not draining

That is a question for Steve VW, because he has an 86 Barth Regal stored in mothballs.

I am not familiar with the Springline rv, but:

My Regal has the tanks on the driver side. The sewer connection has a wye to join each tank to the outlet. Each leg of the wye has an adjacent valve to drain each tank. Easy to find.

It sounds like your valve may be hidden somewhere. If you find the tanks, follow downhill, you should find valve(s)
Some RVs, typically slide in campers and Class C coaches, have only one tank for black/grey and one valve. Some have separate tanks and valves.

If the tank has not been drained for a long time, the contents may have turned more solid and won't drain well. This is why we try to dump tanks after a drive, to slosh the contents around. Same reason when parked, rather than leave the drains open all the time, let the tanks fill and drain them all at once to help "move the mail". Otherwise you may end up with a paper pyramid piled up below the toilet pipe.

If that is the case you may have to snake the pipes out.

good luck, it's a dirty job but someone has to do it!

If the 2 tanks drain into a single outlet, drain the black water first, then the gray water will help rinse the hose.

My 86 regal has 'em just as Steve described as well.