dump release?
 

ok so I notice on my 1980 hi lo there is at least one holding tank in the rear. it's right under the bathroom it seems and there are two pipes running driffrent ways to the outlet. one is suppose to be for waste from restroom and other from sink and shower correct?
I guess if I open the one for the sink water and turn on the sink and water comes directly out then I would know there's no tank for that water...

it has a tank on the front for fresh water cause there is a door your suppose to open to fill. being a 80 they never had the key for it. wish people over years would keep up with things but some dont.

was going add a pic but it's not letting me.right now I had that issue yesterday

if I'm reading you correctly you have two gray water pipes to the small valve and the black water tank to the large valve. Normally the gray water from the kitchen and the bathroom sink and shower go to the gray tank. And only the waste from the toilet goes only into the black tank. Neither of the two should mix.

Go to Video #12 to see the instruction for the tank drains: https://www.hilotrailerforum.com/f49/...-youtube-1233/

You can probably get a generic key for the hatch, they are usually all the same. You may have to check with an RV dealer or supplier. I could be key number 751CH.

Tank valve maintenance
 

After one HiLo told DH a tale of woe about his black and grey tank.He realized it is a good idea to lubricate the valves that you pull to empty them. A little lubrication helps them to slide without binding. He possibly used Silicone spray or a dry lube spray.

So everything that slides should get lubed I guess..I will spray them, I am scared to open it as never know what might be inside the tanks? I don't smell anything (90 degree heat would say that's a good thing) but you never know. Any suggestions on opening them where to do so? or just pray there empty and clean

Just my thoughts..I see PVC, which tells me it's been up-dated or repaired. should be two tanks going into one outlet. Each tank should have it's own slide valve. You would normally remove a cover, open your BLACK tank first then open the slider for the greay tank. After draining is complete, you shut both sliders and put the cover on.
It appears your has been modified to omit the slider or both sliders. Not good, in my opinion.
Tree

White pipe is coming straight from.the black tank in rear.. I should taken pic on both sides but on the left side of the big white pipe is a smaller pipe with the other release in line.

The smaller pipe should be coming from your grey tank then. Follow the dumping procedure Tree gave you.

- Jack

Thanks Jack.

Chris