Some clues are downright obscure but most have at least a slight connection with caving.
Alternatively, they are as disgusting as possible.
There will be a prize for the first correct solution posted to me.

Solution in the next Pelobates

ACROSS

1 Entrances within the gonad itself (5)
4 Descending device manufactured from seaweed? (5)
8 Edward returns, explosively (3)
11 There’s no shortage of it underground (8)
12 Deciphers the slav rune (8)
13 Post docs in a night out on the beer (12,5)
17 Keep your head down in flat-out passage! (3,3)
19 Split (6)
21 Defunct club (5)
22 Cross back bearings about a religious group (6)
23 Archimedes’ ejaculation in Lancaster/Easegill (6)
24 Where most of the water flows (10,7)
31 Not the cave to be in without a good length of rope (4,4)
32 Classic pot; one thousand ringed by a small hobbit (8)
33 Gland found in more than one type of formation (3)
34 Fragile cave in the Little Neath area? (5)
35 Welsh river running undergound, we hear (5)

DOWN

2 Birds commonly seen underground (5)
3 Steps around Hugh initially to manufacture fibres (7)
5 Compensation for having to change clothes again (7)
6 Beg the king to enter the hole (5)
7 Make a grab at the American girl’s crutch (6)
8 Cannabis failing to come up to expectations? (14,3)
9 Thor’s underground storage dump (12,5)
10 Sounds like an extra loud warning of falling rocks (6)
13 Does he make progress in a Yorkshire cave? (7)
14 GR SN9117 1243 (4,3)
15 Mistakes for erections (4,3)
16 Soft drink seemingly made from speleogenetic rock (7)
18 The anti-hero of Tom Sharpe’s ‘Riotous Assembly' (3)
20 Has been spotted in caves on Nordic expeditions (3)
25 Ring compound? (6)
26 The ultimate climbing protection (3,4)
27 Tissue worn by everyone under the wetsuit (7)
28 Sounds attractive, but it’s not cave bearing rock (5)
29 Painful crawl (5)
30 Drunk in a small passage (5)