The bottom pipe is just a go thru pipe by HDB for what reason I not sure, probably some emergency drainage, I attached a pic.
So much rubbish dropped onto my aircon ledge, very frustrating. Buying a long rubbish picker can solve but troublesome to keep the picker, waste space.
The top pipe u mentioned comes with HDB and I think it is because some water heater needed the discharge pipe, it just goes to the floor straight down, however I prefer it to go straight down the drainage and since i am doing a overlay of flooring, i made a copper pipe extension which hide under the tiles and goes to the drainage, my heater does have a small pipe which they just insert it inside without sealing, it is just a discharge pipe for them to drain water for cleaning the drum i think
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I also realised the black mould on the silicon of the aircon piping cover cannot be remove even if I shrub very hard with anything cleaner. Need to buy silicon mold cleaner to get the black stuff off. I got it from supersteam which sell very useful cleaning stuff at affordable price. I love their Ultra33+ wash cloths, cheap at $10.70 for 10 and very absorbing. Ultra88 at $2 each for cleaning glass, I dry dry clean my shower mirror and all the watermark is gone even though the cloth is dry it is able to remove all watermark. Buy it if you getting some stuff from them. I also bought magic bright 503 from them which remove the limescale stain on my shower tiles which I have trouble cleaning. Very strong cleaner which is bad if u touch marble or granite will damage it but gets all floor stain on tiles very clean.