Integrated Sensing and Communication (ISAC) is a key technology for 6G. Bistatic sensing has become a focal topic in 3GPP ISAC discussions, thanks to its advantages such as the absence of self-interference, full reuse of communication equipment and protocols, and path loss gains in certain scenarios. However, in practical systems, bistatic sensing is hindered by time-frequency asynchrony between the transmitter and receiver, including timing offset, timing drift, carrier frequency offset, and random phase noise. Such asynchrony leads to severe target detection errors and introduces significant measurement inaccuracies, critically constraining the practical deployment of bistatic ISAC. Traditional solutions, which rely on line-of-sight (LOS) paths or reference paths, fail to meet the sensing requirements of 6G ISAC, especially in non-line-of-sight (NLOS), rich multipath, and low signal-to-noise ratio (SNR) scenarios. To address this challenge, we propose a comprehensive solution comprising the asynchronous delay-Doppler (ADD) method and the enhanced round-trip measurement (eRTM) method. The proposed scheme is fully compatible with 5G/6G signals and processing architectures, offering advantages such as multiple-scenario adaptability, low computational complexity, and relaxed hardware requirements. Prototype tests demonstrate that it achieves centimeter-level positioning accuracy for passive sensing targets, with performance approaching that of ideal synchronization.