16a. Hollow-sounding inner tube (4) -e - n
21a. Check where you park, say. (4) - - r -
19d. Bill's car vandalised in African port (5) a - - - a
Easy.
4d. Bombarding enemy plane (6) r - i - e -
20a. Garden watering accessory 4-4 (I had hose-pipe but 6 down is epitomize I think making 20 a. - o -e - e - -.
18d. See through material (5) - - - s -
All help appreciated.