We have undertaken the largest survey for outflows within the Galactic plane using simultaneously observed ^13^CO and C^18^O data. Out of a total of 919 ATLASGAL clumps, 328 have data suitable to identify outflows, and 228 (69%+/-3%) show high-velocity outflows. The clumps with detected outflows show significantly higher clump masses (M_clump_), bolometric luminosities (L_bol_), luminosity-to-mass ratios (L_bol_/M_clump_), and peak H_2_ column densities (N_H2_) compared to those without outflows. Outflow activity has been detected within the youngest quiescent clump (i.e., 70{mu}m weak) in this sample, and we find that the outflow detection rate increases with M_clump_, L_bol_, L_bol_/M_clump_, and N_H2_, approaching 90% in some cases (UC HII regions = 93%+/-3%; masers = 86%+/-4%; HC HII regions = 100%). This high detection rate suggests that outflows are ubiquitous phenomena of massive star formation (MSF). The mean outflow mass entrainment rate implies a mean accretion rate of ~10^-4^M_{sun}_/yr, in full agreement with the accretion rate predicted by theoretical models of MSF. Outflow properties are tightly correlated with M_clump_, L_bol_, and L_bol_/M_clump_ and show the strongest relation with the bolometric clump luminosity. This suggests that outflows might be driven by the most massive and luminous source within the clump. The correlations are similar for both low-mass and high-mass outflows over 7 orders of magnitude, indicating that they may share a similar outflow mechanism. Outflow energy is comparable to the turbulent energy within the clump; however, we find no evidence that outflows increase the level of clump turbulence as the clumps evolve. This implies that the origin of turbulence within clumps is fixed before the onset of star formation.