Filter standpipe (inside) joint sealant/caulk? Need to re-seal, unsure what product.

[threecheese]

I've had DE getting into our pool since last summer, and have finally found the culprit (after fixing a suction-side leak, replacing o-ring, then grids, then the manifold).
The caulk on the far side of the standpipe had come off.



I have to remove this caulk and re-seal the pipe to the elbow, does anyone know what exactly the correct compound/procedure is?

You can sorta see it, out of focus, in the other attached image.

 

[threecheese]

Hrm, everything appears to be PVC. Blue cement???

P16_zps0b6bab08.jpg Photo by jblizzle_tfp | Photobucket

 

[threecheese]

Well, if anyone is curious, I bonded the pipe and elbow together with pvc cement, but the fit was way too easy so I supplemented it with plumber's epoxy. I fit it together, it's running, and I will update here once I determine if the fix worked or not.