Is it possible to take off the sunroof glass. It's jammed, goes up but not backwards and I think my pipes are blocked
If I take the glass out will I be able to get to the drain holes ?

this has been copied from the workshop manual [rave] link is in the wiki.. probably your answer is there.

Click image to enlarge

 Discovery 4 HSE
1998 110 TUM HS FFR Hard Top XD WOLF
1982 Series 3 Hard Top

*Gone:L462 D5 HSE LUX, L663 Defender 110 HSE, Discovery 3 HSE, 2014MY Range Rover Sport 5.0 Supercharged AB Dynamic; L405 Exec Vogue SE 4.4, 5.0 Supercharged Autobiography, Defender TDCi XS CSW, Defender TD5 HT, Vogue SE TDV8, Vogue TD6, RRSport SC 4.2V8, Classic 3.9 Vogue Auto, Land Rover Series 3 SWB

I`m just a very starter with FF and car mechanics as well. But following orders of Rave manual was so straightforward, that I could finish with the whole process within half hour.
Here it goes:

Roof Opening Panel - Roof Opening Panel Glass
Removal and Installation
Removal
1. Open the roof opening panel shield.
2. Raise the roof opening panel glass.
3. Release the upper edges of the RH and LH roof opening panel side trims.
4. Remove the RH and LH roof opening panel side trims.
Release the front of the RH and LH roof opening panel side trims and slide forwards.
5. Remove the roof opening panel glass.
Remove the 6 screws.
Installation
1. Install the roof opening panel glass.
Tighten the screws to 6 Nm (4 lb.ft).
2. Align the roof opening panel glass to the roof. For additional information, refer to: Roof Opening Panel Alignment (501-17 Roof Opening Panel, General Procedures).
3. Install the RH and LH roof opening panel side trims, starting with the rear ends.
4. Secure the upper edges of the RH and LH roof opening panel side trims 4.4 TDV8 Vogue Buckingham Blue MY12
from Hungary

thanks