After years, my drain to the upstairs shower is partially clogged and needs to be cleared. Is there any safe drainage cleanser for the black PE pipes. I also have some PVC pipes, could the same cleaner be used for these also?

Have you tried using a plunger. If you pour hot water down the drain first it helps.

Being Thailand there will probably not be any vent pipes so using a good plunger normally does the trick.

I donf't think they make 3-4 metre long plungers do they? There is a clog between upstairs shower drain and the ground floor. 2nd floor is 4 metres above ground floor.

I donf't think they make 3-4 metre long plungers do they? There is a clog between upstairs shower drain and the ground floor. 2nd floor is 4 metres above ground floor.

The plunger doesn't have to be 3-4m long, as long as the pipe is full of water and there's nowhere for the pressure to escape it's worth a plunge.

Following these tips may help you. I doubt you have the P trap though as most Thai plumbers do not install them unless pushed to do it.

Drain Clearing

Turn the shower on and get out that plunger! And I just have to ask....Are you sure the clog is not right underneath the shower drain cover? It's real easy for hair to clog up this area right at/underneath the drain cover. If you haven't already, lift up the drain cover and check/clean that area. If that area is OK, then leave the drain cover off as you do the plunger action.

Problem solved. I managed to pry off the drain cover after years of not attending to it and looked in to find a large amount of mineral buildup. 10 minutes of removing the minerals and the water is draining well again. The plunger would have to have to been a special one as the drain is below the shower seat and is not more than 20 cm below the bottom of the seat, so access was tough enough even with a screwdriver. All is good now though!