Across:
   1. Disaster with large interruption to sustenance (5)
   4. Give up in draw with ref Alf strangely rotten (6 3)
   9,16dn. Has gloop in colon? I suspect this is what killed thirteen in the 1 across after the 21 27 8 (7 9)
  10. He could paint over me, erasing part (7)
  11. Place where doctor treating 9 16 hails pot abuse? (8)
  12. Removing golf club's first water hazard? (5)
  15. Turn back for quantities of 9 (4)
  17. Detective ignoring leads to verify everyone who started it (10)
  18. Perhaps 15 of 27 sniff trees out (10)
  20. Spark needed to have joint (4)
  22. Very relaxed states can offer marijuana as season starts (5)
  23. see 5 down
  27. Product with 9 is king in dairy produce (7)
  28. Set one soul free (7)
  29. Inexpert, I lag, embattled holding back quantity of drink, lost in 21 27 8 (9)
  30. Approaches snare carefully (5)
Down:
   1. Dandy quality shines in Alf's ensemble (10)
   2. Oscar upset some wildlife (5)
   3. Author AI turned, the blooming thing! (6)
   4. Once again memorising unusual liner range (10)
   5,23ac. Have fun... do sit around with so many hogsheads lost in 21 27 8 of '75 (4 8)
   6. Tempting to eat third bit of cake which is hanging around (7)
   7. Indulged too much, and no tea ever cooked (9)
   8. Sack which may be beaten with sack? (4)
  13. A lot sitting idle here, so other use developed (10)
  14. Sends flier out, as unpopular (10)
  16. see 9 across
  19. Racehorse of rank "elite" provided (7)
  21. City reportedly growin' twofold? (6)
  24. Smell where all roads lead in Italy? (5)
  25. What people may have done in 1 across ... turned gaping mouths! (4)
  26. Growth of sticky mess with a thousand and one let go (4)
Solution:
FLOOD=RAFFLEOFF|
L=R=A=E=I=U=V=I|
ALCOHOL=VERMEER|
S=A=L=E=E=K=R=E|
HOSPITAL=RIVER=|
I===A=R=S=N=A=F|
NIPS=INSTIGATOR|
E=O===I=O===E=I|
STIFFENERS=KNEE|
S=S=R=G=E=D===N|
=COMAS=THOUSAND|
S=N=N=C=O=B=R=L|
WHISKEY=UNLOOSE|
A=N=E=S=S=I=M=S|
MEGALITRE=NEARS|
Name: 855 - Colon Gloop
Author: by BenDR