洞

cave / hole / zero (unambiguous spoken form when spelling out numbers) / CL:個|个[ge4]

洞 = 同 + 氵 : Doggy Dog (du) finds two twins (同) have fallen down the cave (洞) in the engine's bathroom ((e)ng4). He immediately begins to dig a tunnel to bring them a bottle of water (氵) until more help arrives.

洞 character breakdown

洞
- 同
  - 冂
    - 丨
    - ㇆
      - 一
      - 亅
  - 𠮛
    - 一
    - 口
- 氵
  - ⺀
    - 丶
  - ㇀

同

tóng = tu + (e)ng2

like / same / similar / together / alike / with

同 = 冂 + 𠮛 : Tommy Turtle (tu) is stapling (冂) a magical scroll (𠮛) to the wall of the engine's kitchen ((e)ng2). On it he wrote that he's looking for two twins (mnemonic symbol for 同).

氵

shuǐ = shu + ei3

"water" radical in Chinese characters (Kangxi radical 85), occurring in 沒|没[mei2], 法[fa3], 流[liu2] etc / see also 三點水|三点水[san1 dian3 shui3]

氵 = ⺀ + ㇀ : Mnemonic symbol: a bottle of water. Sheldon Shrimp (shu) enjoys a bottle of water (氵) in the Eiffel Tower's living room (ei3). The got the water by scratching (㇀) a blossom (⺀) and catching the leaking dew in a bottle.

同

衕

tòng = tu + (e)ng4

see 衚衕|胡同[hu2 tong4]