Elliott From 'E.T.' Filled Urine Sample with Water After DUI, Cops Suspect

Elliott from 'E.T.' allegedly tried to pull a fast one during his Oregon DUI stop by brazenly tampering with his urine test, then playing it cool in hopes of passing a blood alcohol test.

Henry Thomas refused to complete breathalyzer and field sobriety tests ... according to the Tualatin PD report on his October DUI arrest, and instead, he was taken to the station for a urine test.

In the report, obtained by TMZ, cops say they placed the actor in a holding cell before requesting the urine sample. As an officer was reading Henry the consent form, cops say he interrupted, asked for the cup and went over to the toilet to get down to biz.

Police say the officer turned her back to Thomas' cell and continued reading the consent form, and heard him taking a leak. But, when he returned the cup, cops say it was not warm and the sample was completely clear and filled to the brim.

Cops asked Thomas if he tampered with the urine sample by dipping it into the toilet, and he denied it.

As we first reported, Tualatin cops responded to a call of Thomas being asleep at the wheel in the middle of an intersection, and say they found 'fast acting THC' in his car.

Anyway, cops say while they were transporting Thomas to a hospital for a blood test, he threatened to sue the police department and the city ... and bragged about being the child star from 'E.T.'

He got one more chance to provide another urine sample at the hospital, but police say the actor claimed he didn't have to pee and again insisted he didn't tamper with the earlier sample.

But, just like Steven Spielberg's iconic 1982 film, there's a happy ending for Elliott.

IF he cheated the pee test, he never got busted for it, because he took a sweet plea deal and won't spend any time behind bars.