>Can I sand out th pre stain, if so what grit?

Wait for it to fully dry first, then yes you can sand it off (or more accurately, sand off the wood from the surface that has absorbed the product).

Almost every "pre-stain" or "conditioner" product is in essence just thinned finish, so largely it won't be coating the surface of the wood but instead will be absorbed into the surface wood fibres.

After reading the full Answer, if you still want to remove it all, this will require more sanding than you're expecting — both in terms of how much sanding will be required, and how coarse the abrasive you use to begin with. 

In essence the process will be similar to how you'd fully sand any wood from scratch, beginning by sanding at a coarse grit to remove the bulk of the wood you need to remove, then progressively sanding finer until you're at your final grit. So for example:

* Start at 80.
* Then sand with 120 or 150 (this would normally be your intermediate grit) *until all the 80-grit sanding scratches are removed, and no more*.
* Normally you would then sand with your final grit (180 or 240) but because you're staining the rule of thumb is you don't sand as finely, because sanding scratches allow the wood to hold on to more stain. So 150 may be as fine as you want to go, although 180 may be the grit recommended in certain cases.

**Note:** assuming you sanded with any type of rotating sander as is so common these days, you should complete sanding by hand-sanding in the direction of the grain with the same grit as the last power sanding. This manual sanding step should be thorough enough to remove all traces of rotational sanding marks, especially 'pigtails', that might be present because they are highlighted by stain, not obscured.

However....

**Sanding might not be needed**  
Without photos of the pooling we can't be sure what it was like or how extensive it was. But regardless, there is a chance no sanding will be needed.

This is because there's a possibility that an incompatibility between the "pre-stain" and the oil-based stain is the cause of the problem here – at least after only 15 minutes. So it is worth trying the stain a second time, after the first product has had a chance to fully dry. And you're waiting for that anyway, or the time has already passed :-)