Idea's on slow draining sink.

[Rorschach]

Upstairs bathroom sink drains very slowly. Nothing blocking the plug hole, being a bathroom it does get biofilm buildup around the drain but I clean this regularly, looking down into the trap now it is spotless white pipe.
Plunging seems to make a difference but only for a few days and then it slows again.

Any ideas before I start stripping out the waste pipe?

[big-all]

do you have people using the sink with long hair ??

[kellys_eye]

Greasy gunge - usually non-dissolved soapy products. I'm guessing your trap isn't the standard u-bend but one of those 'compact' straight versions???

I use the palm of my hand to give it a 'plunge' every couple of days and it tends to keep it clear.

[Rorschach]

do you have people using the sink with long hair ??

Not particularly long. A strainer is used to trap hair. Some does make it to the gully but I clear that often too.

Greasy gunge - usually non-dissolved soapy products. I'm guessing your trap isn't the standard u-bend but one of those 'compact' straight versions???

I use the palm of my hand to give it a 'plunge' every couple of days and it tends to keep it clear.

No it's a standard U bend and it's perfectly clean at the trap end. I guess the problem must be further down the line.

[wine~o]

You could try caustic soda, careful though as it needs handling with caution.

(do not confuse caustic soda with soda flakes)

[Rorschach]

I have plenty of caustic soda on hand, will give that a try.

[Someone-Else]

Its a bit late now, but DO READ THE INSTRUCTIONS.

You mix it in a bucket of HOT water then pour it down said plug hole. If you pour it in cold, it can set like concrete. (No, it wasn't me, but I lent him a drill to drill holes through it, and it worked)

[Rorschach]

NOOOO you never add caustic soda to HOT water!

[Razor]

NOOOO you never add caustic soda to HOT water!

You can add it slowly to hot water but you can't add hot water to caustic soda.

Used tons of it on 2 stroke exhaust when I was a lad