Tanko joined German side BV Borussia Dortmund from King Faisal Babes at age 17, making him the third youngest player to appear professionally for the team, behind Nuri ?ahin and Lars Ricken. He made his Bundesliga debut on 24 September 1994, in a 5–0 home win against VfB Stuttgart, and finished his debut season with 14 games and one goal.

Injuries and loss of form led to an eventual release from the club (he did participate in three contests, all as a late substitute, in Borussia's 1996–97 UEFA Champions League victorious run) as he amassed no more than three league appearances in three different seasons, also being suspended and eventually released after testing positive for cannabis.

In January 2001, Tanko joined fellow league side SC Freiburg, scoring in his fourth game, a 3–1 win at VfL Bochum, but also missing a great part of the following campaign due to a severe knee injury,[2] as the Black Forest team dropped down to the second division.

At Freiburg, Tanko's output improved slightly, and he played a career-high 27 matches (with two goals) in 2005–06's second level. However, he only appeared once the following season, and retired at 30.

On 1 July 2007, Tanko was named assistant coach for Freiburg's reserves, leaving after 18 months, together with Karsten Neitzel, to J. League's Urawa Red Diamonds, in the same capacity, as he rejoined former Freiburg boss Volker Finke.